The prior art gear sets are used in bicycle. FIGS. 1, 2, and 3 shows a prior art structure. The gear set 10 includes a first gear 11, a second gear 12, and a third gear 13. Each gear 11, 12 and 13 is punched with a plurality of teeth 24, a plurality of recess portions 25 and a plurality of rivet holes 16. Then sleeves 17 and rivets 18 serve to rivet the first, second and third gears 11, 12 and 13. The first gear 11 has a via hole 110 and the second gear 12 has an assembled hole 120 for assembling the treading sheet 19 of the pedal. The prior art has the following disadvantages. (1) Each gear is formed individually and then the sleeves 17 and rivets 18 are assembled. The assembled work is tedious and complicated so that the cost is high. The combination of sleeves 17 and rivets are loose so that after a long time, the gears will loose. The connection of rivets 18 are point connections so that the combination of gears is not firmly. Gaps are formed between gears so that a released chain will fall into the gap. All the actions are applied upon the teeth 14 and the concave portions 15. The gear is easily worn.